Double layer oxide cathode with reducing agent



July 25, 1967 H. J. LEMMENS ETAL 3,

DOUBLE LAYER OXIDE CATHODE WITH REDUCING AGENT Original Filed March 2, 1962 INVENTORS HEN omclws ILEMMENS PIETER ZA M aw N United States Patent 3 Claims. (51. 313-346) This application is a continuation of application Ser. No. 177,042 filed Mar. 2, 1962, now abandoned.

The invention relates to an electric discharge tube comprising a cathode, the outer side of which consists of barium-activated alkaline earth metal oxides, this activated layer and the metal cathode body having provided between them a layer of oxidic alkaline earth metal compounds containing barium and, in addition, a reducing agent which releases barium from the oxidic compounds in the operation tube.

With a known cathode a metal gauze is arranged between the two oxidic layers, which gauze establishes a contact with the metal cathode body and performs the function of a current supply member for the emissive outer layer. The capacity of these cathodes exceeds considerably that of the conventional oxide cathodes, in which a layer of alkaline earth metal oxides obtained from carbonates is applied to a nickel cathode body, containing reducing admixtures. With these last-mentioned cathodes a so'called intermediate-layer resistance is formed during the use of the tube owing to the reaction of the oxidized reducing admixture and the alkaline earth metal oxide and owing to diffusion of the free barium to the surface.

The known cathodes comprising two oxidic layers separated by a metal gauze have, however, the disadvantage of a slightly more complicated structure and hence of a higher price.

The invention has for its object to provide a cathode which is more advantageous than the known cathodes.

In accordance with the invention in an electric discharge tube comprising a cathode, the outer side of which consists of barium-activated alkaline earth metal oxides, this activated layer and the metal cathode body having arranged between them a layer of oxidic alkaline earth compounds containing barium and, moreover, a reducing agent releasing barium from the oxidic compounds in the operation of the tube the activated oxide layer is applied directly to the layer containing the reducing agent.

It has been found, that if the layer adjacent the metal cathode body contains an adequate quantity of reducing agent, this layer does not form an intermediate-layer resistance in the operation of the tube, while the activation of the top layer is sufficient for attaining a long life-time with high current density.

The top layer contains preferably strontium oxide, since with higher temperatures this remains porous for a longer time than barium oxide alone, or it contains a mixed oxide of barium and strontium, whereas the substratum contains a double or triple alkaline earth metal oxide with titanium as a reducing agent, which is added in the form of titanium hydride during the manufacture of the 3,333,141 Patented July 25, 1967 cathode. The manufacture of cathodes according to the invention is not more difiicult than that of the conventional oxide cathodes, since only layers of a few microns in thickness are formed during each spraying operation, so that a layer of a few tens of microns is obtained only after many spraying operations.

The support of the layers is a cathode body preferably consisting of galvanic nickel or cobalt without admixtures. Apart from its slightly higher price, cobalt has the advantage that it has only half the evaporation rate of nickel.

The invention will now be described more fully with reference to the accompanying drawing, which shows a cathode body with activated layers according to the invention.

Referring to the drawing, reference numeral 1 designates a nickel tube, on which a nickel hood 2 having a wall thickness of 0.1 mm. is welded. This hood consists of galvanic nickel without admixtures. Onto the hood 2 is sprayed a layer 3 of barium-strontium carbonate of 60,11. in thickness, containing 3% by weight of titanium hydride. Onto this layer 3 is sprayed a layer 4 of calciumstrontium carbonate of 20 1. in thickness without any admixture. After the cathode has been provided with a filament body and mounted in the tube, the carbonates are decomposed by heating into oxides, also the titanium hydride being then dissociated into metallic titanium.

With test diodes the cathodes described above yielded, with a current density of 1.5 A./cm. lifetimes from 1200 to 1500 hours and with a current density of 1 A./cm. lifetimes from 2000 to 2500 hours. It should be noted, in addition, that with a test diode the results will, in general, be less favorable than with normal tubes, since in a test diode the anode usually has a higher temperature. The lifetimes indicated above apply to a cathode temperature of 760 C. The top layer may also consist of bariumstrontium-calcium carbonate.

What is claimed is:

1. A cathode for an electron discharge device comprising a support of a metal selected from the group consisting of nickel and cobalt, an outer layer of a barium activated alkaline earth metal oxide, and a layer intermediate the outer layer and the support and in direct contact with the outer layer consisting of alkaline earth oxidic compounds containing barium and metallic titanium as a reducing agent.

2. A cathode as claimed in claim 1 in which the outer layer contains strontium oxide.

3. A cathode as claimed in claim 2 in which the intermediate layer contains at least two alkaline earth metal oxides.

References Cited UNITED STATES PATENTS 2,945,150 7/1960 Desantis et a1. 3 13-346 2,950,993 8/1960 Umbreit 313-346 2,995,674 8/1961 Apelbaum et a1. 313-346 X 3,156,844 11/1964 Veith 313346 X 3,159,461 12/1964 Macnair 313-346 FOREIGN PATENTS 164,984 8/1953 Australia.

JOHN W. HUCKERT, Primary Examiner.

JAMES D. KALLAM, Examiner.

A. J. JAMES, Assistant Examiner. 

1. A CATHODE FOR AN ELECTRON DISCHARGE DEVICE COMPRISING A SUPPORT OF A METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALT, AN OUTER LAYER OF A BARIUM ACTIVATED ALKALINE EARTH METAL OXIDE, AND A LAYER INTERMEDIATE THE OUTER LAYER AND THE SUPPORT AND IN DIRECT CON- 